Yeomai
e94dfb9e35
B. 二分定位 + 邻域采样（我推荐） 把配置的语义从"这就是要生成的 10 档"改成"允许搜索的参数梯度"（比如分辨率梯度、帧率梯度、质量梯度三张表）。运行时： 1. 用每个组合只编 2 帧的方式粗估体积（很便宜）； 2. 靠单调性做二分，几轮就找到"体积刚好不超过目标"的参数点； 3. 在这个点周围取 10 个组合（略高、略低各几个），完整生成。 成本大概是十几次估算编码 + 10 档完整编码，和现在基本持平甚至更省（估算只编 2 帧）。效果是候选真正围绕你输入的目标分布——比如你填 30 KB，出来的就是 22、26、29、31、35 KB 这种，而不是 5 KB 和 300 KB 各一个。 代价是你现在这套配置格式要推翻重做——从"精确档位表"变成"参数范围表"
79 lines
3.1 KiB
JavaScript
79 lines
3.1 KiB
JavaScript
'use strict';
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function writeUint24LE(buffer, offset, value) {
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buffer[offset] = value & 0xff;
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buffer[offset + 1] = (value >>> 8) & 0xff;
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buffer[offset + 2] = (value >>> 16) & 0xff;
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}
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function chunk(type, payload) {
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const padding = payload.length & 1;
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const output = Buffer.alloc(8 + payload.length + padding);
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output.write(type, 0, 4, 'ascii');
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output.writeUInt32LE(payload.length, 4);
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payload.copy(output, 8);
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return output;
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}
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function frameData(webp) {
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if (!webp) throw new Error('WebP 帧数据缺失');
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const input = Buffer.from(webp);
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if (input.length < 20 || input.toString('ascii', 0, 4) !== 'RIFF' || input.toString('ascii', 8, 12) !== 'WEBP') {
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throw new Error('Invalid WebP frame');
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}
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const parts = [];
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let hasAlpha = false;
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let offset = 12;
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while (offset + 8 <= input.length) {
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const type = input.toString('ascii', offset, offset + 4);
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const length = input.readUInt32LE(offset + 4);
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const end = offset + 8 + length + (length & 1);
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if (end > input.length) throw new Error('Truncated WebP frame');
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if (type === 'ALPH' || type === 'VP8 ' || type === 'VP8L') parts.push(input.subarray(offset, end));
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if (type === 'ALPH') hasAlpha = true;
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offset = end;
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}
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if (!parts.some((part) => part.toString('ascii', 0, 4) === 'VP8 ' || part.toString('ascii', 0, 4) === 'VP8L')) {
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throw new Error('WebP frame has no image data');
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}
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return { data: Buffer.concat(parts), hasAlpha };
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}
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function encode(options) {
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const width = Number(options && options.width);
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const height = Number(options && options.height);
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const frames = options && options.frames;
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if (!Number.isInteger(width) || width < 1 || width > 0x1000000 || !Number.isInteger(height) || height < 1 || height > 0x1000000) {
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throw new RangeError('Animated WebP dimensions are invalid');
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}
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if (!Array.isArray(frames) || frames.length < 2) throw new RangeError('Animated WebP requires at least two frames');
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const preparedFrames = frames.map((frame) => ({ frame, ...frameData(frame.webp) }));
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const vp8x = Buffer.alloc(10);
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vp8x[0] = 0x02 | (preparedFrames.some(({ hasAlpha }) => hasAlpha) ? 0x10 : 0);
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writeUint24LE(vp8x, 4, width - 1);
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writeUint24LE(vp8x, 7, height - 1);
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const anim = Buffer.alloc(6);
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const background = options.background || [30, 30, 30, 255];
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anim.set([background[2] || 0, background[1] || 0, background[0] || 0, background[3] === undefined ? 255 : background[3]], 0);
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anim.writeUInt16LE(Math.max(0, Math.min(0xffff, options.plays || 0)), 4);
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const chunks = [chunk('VP8X', vp8x), chunk('ANIM', anim)];
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for (const { frame, data } of preparedFrames) {
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const header = Buffer.alloc(16);
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writeUint24LE(header, 6, width - 1);
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writeUint24LE(header, 9, height - 1);
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writeUint24LE(header, 12, Math.max(1, Math.min(0xffffff, Math.round(frame.duration))));
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header[15] = 0x02;
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chunks.push(chunk('ANMF', Buffer.concat([header, data])));
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}
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const body = Buffer.concat([Buffer.from('WEBP'), ...chunks]);
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const output = Buffer.alloc(8 + body.length);
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output.write('RIFF', 0, 4, 'ascii');
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output.writeUInt32LE(body.length, 4);
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body.copy(output, 8);
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return output;
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}
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module.exports = { encode };
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